U.S. Department of the Interior
National Park Service
Preservation Assistance Division
Washington, D.C.

An illustrated booklet addressing the Secretary's Standards and the
guidelines is available from the U.S. Government Printing Office.
The title is "The Secretary of the Interior's Standards for
Rehabilitation & Illustrated Guidelines for Rehabilitating Historic
Buildings", ISBN 0-16-035979-1.

Each of the guidelines included in the booklet mentioned above have
been separated into individual entries for specific use in HBPP.
This entry represents one of many guidelines included in the
booklet and describes RECOMMENDED and NOT RECOMMENDED applications
of the Secretary of the Interior's Standards as they relate to
Mechanical Systems. For a list of the Secretary of the Interior's
Standards for Rehabilitation, see 01091-04-S; For general
information relating to the purpose, organization and content of
the individual guidelines, see 01091-05-S. Both of these entries
should be referenced along with the information contained in this
document.

The visible features of historic heating, lighting, air
conditioning and plumbing systems may sometimes help define the
overall historic character of the building and should thus be
retained and repaired, whenever possible. The systems themselves
(the compressors, boilers, generators and their ductwork, wiring
and pipes) will generally either need to be upgraded, augmented, or
entirely replaced in order to accommodate the new use and to meet
code requirements. Less frequently, individual portions of a
system or an entire system are significant in the history of
building technology; therefore, the identification of character-defining
features or historically
significant systems should take
place together with an evaluation of their physical condition early
in project planning.

IDENTIFYING, RETAINING AND PRESERVING

1. Recommended:

- Identifying, retaining, and preserving visible
features
of early mechanical systems that are
important in
defining the overall historic character
of the building,
such as radiators, vents, fans, grilles,
plumbing
fixtures, switchplates, and lights.

Not Recommended:

- Removing or radically changing features of
mechanical
systems that are important in defining
the overall
historic character of the building so
that, as a result,
the character is diminished.

PROTECTING AND MAINTAINING

1. Recommended:

- Protecting and maintaining mechanical, plumbing,
and
electrical systems and their features
through cyclical
cleaning and other appropriate measures.

Not Recommended:

- Failing to provide adequate protection of
materials on a
cyclical basis so that deterioration
of mechanical
systems and their visible features results.

2. Recommended:

- Preventing accelerated deterioration of mechanical
systems by providing adequate ventilation
of attics,
crawlspaces, and cellars so that moisture
problems are
avoided.

Not Recommended:

- Enclosing mechanical systems in areas that
are not
adequately ventilated so that deterioration
of the
systems results.

REPAIRING

1. Recommended:

- Repairing mechanical systems by augmenting
or upgrading
system parts, such as installing new
pipes and ducts;
requiring; or adding new compressors
or boilers.

Not Recommended:

- Replacing a mechanical system or its functional
parts
when it could be upgraded and retained.

REPLACING

1. Recommended:

- Replacing in kind -- or with compatible substitute
material -- those visible features of
mechanical systems
that are either extensively deteriorated
or are missing
when there are surviving prototypes
such as ceiling fans,
switchplates, radiators, grilles, or
plumbing fixtures.

Not Recommended:

- Installing a replacement feature that does
not convey the
same visual appearance.

NOTE: THE FOLLOWING REPRESENTS PARTICULARLY COMPLEX TECHNICAL OR
DESIGN ASPECTS OF REHABILITATION PROJECTS AND SHOULD ONLY BE
CONSIDERED AFTER THE PRESERVATION CONCERNS LISTED ABOVE HAVE BEEN
ADDRESSED.

ALTERATIONS/ADDITIONS FOR THE NEW USE

1. Recommended:

- Installing a completely new mechanical system
if required
for the new use so that it causes the
least alteration
possible to the building's floor plan,
the exterior
elevations, and the least damage to
historic building
material.

Not Recommended:

- Installing a new mechanical system so that
character-
defining structural or interior features
are radically
changed, damaged, or destroyed.

2. Recommended:

- Installing the vertical runs of ducts, pipes,
and cables
in closets, service rooms, and wall
cavities.

Not Recommended:

- Installing vertical runs of ducts, pipes,
and cables in
places where they will obscure character-defining
features.

- Concealing mechanical equipment in walls
or ceilings in
a manner that requires the removal of
historic building
material.

- Installing air conditioning units if required
by the new
use in such a manner that the historic
materials and
features are not damaged or obscured.

Not Recommended:

- Cutting through features such as masonry
walls in order
to install air conditioning units.

4. Recommended:

- Installing heating/air conditioning units
in the window
frames in such a manner that the sash
and frames are
protected. Window installations
should be considered
only when all other viable heating/cooling
systems would
result in significant damage to historic
materials.

Not Recommended:

- Radically changing the appearance of the
historic
building or damaging or destroying windows
by installing
heating/air conditioning units in historic
window frames.